ASPN Aspen Aerogels Inc

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 3)

Aspen Aerogels, Inc.

(Name of Issuer)

Common stock, par value $0.00001 per share

(Title of Class of Securities)

04523Y105

(CUSIP Number)

Koch Industries, Inc.

4111 East 37^th Street North

Wichita, Kansas 67220

Attn: Raffaele G. Fazio

(316) 828-8310

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

May 14, 2024

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that section of the Exchange Act but shall be subject to all other provisions of the Exchange Act (however, see the Notes).

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Explanatory Note

This Amendment No. 3 (this “Amendment No. 3”) to a Statement on Schedule 13D relates to the shares of common stock, par value $0.00001 per share (“Public Shares”) of Aspen Aerogels, Inc., a Delaware corporation (the “Issuer”), and amends the initial statement on Schedule 13D (the “Initial Statement”) filed by the Reporting Persons identified therein on April 5, 2022, as amended by Amendment No. 1 (“Amendment No. 1”) thereto filed on May 3, 2022 and Amendment No. 2 (“Amendment No. 2”) thereto filed on December 7, 2022 (as amended by Amendment No. 1, Amendment No. 2 and this Amendment No. 3, the “Schedule 13D”). Except as specifically provided herein, this Amendment No. 3 does not modify any of the information previously reported in the Initial Statement, as amended by Amendment No. 1 and Amendment No. 2. Capitalized terms used but not defined in this Amendment No. 3 shall have the same meanings herein as are ascribed to such terms in the Initial Statement, as amended by Amendment No. 1 and Amendment No. 2.

The filing of this Amendment No. 3, and the information contained in the Schedule 13D, shall not be construed as an admission that any of SCC, KIM, KIG, KIGH, or Koch Industries is, for purposes of Sections 13(d) or 13(g) of the Exchange Act, the beneficial owner of any Public Shares covered by the Schedule 13D.

Item 2 of this Statement on Schedule 13D is hereby amended and supplemented as follows:

The information set forth in the amended and restated Schedule A attached to this Amendment No. 3 is incorporated by reference in Item 2 and supersedes the previously filed Schedule A.

Set forth on Schedule A is the name and present principal occupation or employment of each of the directors, managers and executive officers of each Reporting Person as of the date hereof. The business address for each of the directors, managers and executive officers listed on Schedule A, and the name and address of any corporation or other organization in which each such director’s, manager’s or executive officer’s employment is conducted, is c/o Koch Industries, Inc., 4111 East 37th Street North, Wichita, Kansas 67220.

(d)-(e) During the last five years, none of the Reporting Persons nor, to the knowledge of the Reporting Persons, any of the persons listed on Schedule A to the Schedule 13D, (1) has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or (2) has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws, or finding any violation with respect to such laws.

(f) All of the directors, managers and executive officers listed on Schedule A are citizens of, the United States.

Item 4 of this Statement on Schedule 13D is hereby amended and replaced in its entirety by the following:

The responses set forth in Item 3 and Item 6 hereof are incorporated by reference in their entirety.

The Reporting Persons hold the Public Shares and the Notes for investment purposes.

The Reporting Persons review their investment in the Issuer on a continuing basis, and may in the future determine: (1) to dispose of all or a portion of the securities of the Issuer owned by them or (2) to take any other available course of action.

From time to time, the Reporting Persons intend to engage in discussions with the Board of Directors of the Issuer and/or members of the Issuer’s management team concerning a broad range of operational and strategic matters, including, without limitation, the Issuer’s business, operations, capital structure, governance, management, and strategy as well as potential financings, business combinations, strategic alternatives, and other matters concerning the Issuer, including transactions in which the Reporting Persons may seek to participate and potentially engage.

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Notwithstanding anything contained herein, the Reporting Persons specifically reserve the right to change their intention with respect to any or all of such matters. In reaching any decision as to their course of action (as well as to the specific elements thereof), the Reporting Persons currently expect that they would take into consideration a variety of factors, including, but not limited to, the following: the Issuer’s business and prospects; other developments concerning the Issuer and its businesses generally; other business opportunities available to the Reporting Persons; developments with respect to the business of the Reporting Persons; changes in law and government regulations; general economic conditions; and money and stock market conditions, including the market price of the securities of the Issuer.

Except as set forth in this Item 4 of this Schedule 13D Amendment, the Reporting Persons do not have any present plans or proposals that relate to or would result in any of the actions specified in clauses (a) through (j) of the instructions to Item 4 of this Schedule 13D Amendment.

Item 5 of this Statement on Schedule 13D is hereby amended and replaced in its entirety by the following:

The information set forth in or incorporated by reference in Items 2, 3, 4 and on the cover pages of this Schedule 13D Amendment is incorporated by reference in its entirety into this Item 5.

(a) and (b) – As of the date hereof, the Reporting Persons hold 16,232,696 Public Shares, representing approximately 20.3% of the outstanding Public Shares. The percentage of the outstanding Public Shares held by the Reporting Persons is calculated using 80,113,477 Public Shares deemed outstanding as of May 1, 2024, including (i) 76,121,210 Public Shares outstanding as of May 1, 2024 as set forth in the Issuer’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2024 filed with the SEC on May 2, 2024, and (ii) 3,952,267 Public Shares issuable upon conversion of the Notes, which includes Public Shares issuable upon conversion of the principal amount, as increased by payment-in-kind interest payments through, and including, December 30, 2023.

(c) – Except as set forth in this Schedule 13D Amendment, no transactions in the Public Shares were effected by the Reporting Persons, or, to the knowledge of the Reporting Persons, any of the persons listed on Schedule A hereto in the 60 days preceding the date hereof.

(d) – Except as set forth herein, to the knowledge of the Reporting Persons, no other person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, any Public Shares of the Issuer beneficially owned by the Reporting Persons as described in this Item 5.

(e) – Not applicable.

Item 6 of this Statement on Schedule 13D is hereby amended and supplemented as follows:

The information set forth in Item 3 of this Statement is incorporated by reference in its entirety into this Item 6.

Lock-Up Agreement

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Wood River executed a Lock-Up Agreement (the “Lock-Up Agreement”) in connection with its sale of common stock of the Issuer on May 14, 2024. Under the terms of the Lock-Up Agreement, during the period beginning on May 14, 2024 (the “Initial Trade Date”) through and including the date that is the 60th day after the Initial Trade Date (the “Lock-Up Period”), subject to certain carve-outs and exceptions, including with respect to transactions involving the Notes, Wood River will not, and will not cause or direct any of its affiliates to, without the prior written consent of the Representatives, directly or indirectly, (i) offer, sell, assign, transfer, pledge, contract to sell, lend or otherwise dispose of, or announce the intention to otherwise dispose of, any Public Shares or securities convertible into or exercisable or exchangeable for Public Shares, (ii) enter into, or announce the intention to enter into, any swap, hedge or similar agreement or arrangement (including, without limitation, the purchase or sale of, or entry into, any put or call option, or combination thereof, forward, swap or any other derivative transaction or instrument, however described or defined) that transfers, is designed to transfer or reasonably could be expected to transfer (whether by the undersigned or someone other than the undersigned) in whole or in part, directly or indirectly, the economic risk of ownership of Public Shares or securities convertible into or exercisable or exchangeable for Public Shares, whether now owned or hereafter acquired by the undersigned or with respect to which the undersigned has or hereafter acquires the power of disposition, or (iii) engage in, or announce the intention to engage in, any short selling of Public Shares or securities convertible into or exercisable or exchangeable for Public Shares.

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Item 7 of this Statement on Schedule 13D is amended and supplemented by the filing of the following additional documents as exhibits hereto:

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After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: May 16, 2024

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Schedule A

Directors and Executive Officers of Reporting Persons

The following tables set forth the name and present principal occupation or employment of each of the managers, directors and executive officers of the Reporting Persons.

Managers and Executive Officers of Wood River Capital, LLC

Managers and Executive Officers of SCC Holdings, LLC

Managers and Executive Officers of KIM, LLC

Managers and Executive Officers of Koch Investments Group, LLC

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Managers and Executive Officers of Koch Investments Group Holdings, LLC

Directors and Executive Officers of Koch Industries, Inc.

Exhibit 99.1

LOCK-UP AGREEMENT

May 14, 2024

Craig-Hallum Capital Group LLC

Ladies and Gentlemen:

The undersigned proposes to sell shares (the “Securities”) of the common stock of the Company (the “Common Stock”) of Aspen Aerogels, Inc., a Delaware corporation (the “Company”), held by the undersigned or its affiliates (the “Trade”) through Craig-Hallum Capital Group LLC, as agent (the “Agent”).

LOCK-UP

In consideration of the Agent’s agreement to serve as broker for the Trade of the Securities, and for other good and valuable consideration receipt of which is hereby acknowledged, the undersigned hereby agrees that, without the prior written consent of the Agent, the undersigned will not, and will not cause any direct or indirect affiliate to, during the period beginning on the date of the first Securities confirmed for sale in the Trade (the “Initial Trade Date”) and ending at the close of business 60 days after the Initial Trade Date (such period, the “Restricted Period”):

(1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock (including without limitation, Common Stock or such other securities which may be deemed to be beneficially owned by the undersigned in accordance with the rules and regulations of the Securities and Exchange Commission (“SEC”) and securities which may be issued upon exercise of a stock option or warrant) (collectively with the Common Stock, the “Lock-Up Securities”), provided that the PIK Toggle Notes (as defined below) shall not be Lock-Up Securities,

(2) enter into any hedging, swap or other agreement or transaction that transfers, in whole or in part, any of the economic consequences of ownership of the Lock-Up Securities, whether any such transaction described in clause (1) or (2) above (any such transaction, a “Transfer”) is to be settled by delivery of Lock-Up Securities, in cash or otherwise,

(3) make any demand for or exercise any right with respect to the registration of any Lock-Up Securities, or

(4) publicly disclose the intention to do any of the foregoing.

The undersigned acknowledges and agrees that the foregoing precludes the undersigned from engaging in any hedging or other transactions or arrangements (including, without limitation, any short sale or the purchase or sale of, or entry into, any put or call option, or combination thereof, forward, swap or any other derivative transaction or instrument, however described or defined) designed or intended, or which could reasonably be expected to lead to or result in, a sale or disposition or transfer (whether by the undersigned or any other person) of any economic consequences of ownership, in whole or in part, directly or indirectly, of any Lock-Up Securities, whether any such transaction or arrangement (or instrument provided for thereunder) would be settled by delivery of Lock-Up Securities, in cash or otherwise.

The undersigned further confirms that it has furnished the Agent with the details of any transaction the undersigned, or any of its affiliates, is a party to as of the date hereof, which transaction would have been restricted by this Letter Agreement (the “Letter Agreement”) if it had been entered into by the undersigned during the Restricted Period.

As used herein, “PIK Toggle Notes” refers to the Convertible Senior PIK Toggle Notes due 2027 issued to the undersigned, pursuant to that certain note purchase agreement, dated as of February 15, 2022 and subsequently amended by an amendment to the PIK Toggle Notes, dated as of November 28, 2022, as the foregoing may be amended from time to time.

LOCK-UP EXCEPTIONS

Notwithstanding the foregoing, the undersigned may:

(i) as a bona fide gift or gifts, or for bona fide estate planning purposes,

(ii) by will or intestacy,

(iii) to any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned, or if the undersigned is a trust, to a trustor or beneficiary of the trust or to the estate of a beneficiary of such trust (for purposes of this Letter Agreement, “immediate family” shall mean any relationship by blood, current or former marriage, domestic partnership or adoption, not more remote than first cousin),

(iv) to a corporation, partnership, limited liability company or other entity of which the undersigned or the immediate family of the undersigned are the legal and beneficial owner of all of the outstanding equity securities or similar interests,

(v) to a nominee or custodian of a person or entity to whom a disposition or transfer would be permissible under clauses (i) through (iv) above,

(vi) if the undersigned is a corporation, partnership, limited liability company, trust or other business entity, (A) to another corporation, partnership, limited liability company, trust or other business entity that is an affiliate (as defined in Rule 405 promulgated under the Securities Act of 1933, as amended) of the undersigned, or to any investment fund or other entity controlling, controlled by, managing or managed by or under common control with the undersigned or affiliates of the undersigned (including, for the avoidance of doubt, where the undersigned is a partnership, to its general partner or a successor partnership or fund, or any other funds managed by such partnership), or (B) as part of a distribution or other Transfer to the members, partners, shareholders or other equity holders of the undersigned,

(vii) by operation of law, such as pursuant to a qualified domestic order, divorce settlement, divorce decree or separation agreement, or related court order,

(viii) to the Company from an employee of the Company upon death, disability or termination of employment, in each case, of such employee,

(ix) as a sale of shares of Common Stock acquired in open market transactions after the Initial Trade Date,

(x) to the Company in connection with the vesting, settlement, or exercise of restricted stock units, options, warrants or other rights to purchase shares of Common Stock (including, in each case, by way of “net” or “cashless” exercise), including for the payment of exercise price and tax and remittance payments due as a result of the vesting, settlement, or exercise of such restricted stock units, options, warrants or rights, provided that any such shares of Common Stock received upon such exercise, vesting or settlement (other than such shares as are transferred or surrendered to the Company in connection

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with such vesting, settlement or exercise event) shall be subject to the terms of this Letter Agreement, and provided further that any such restricted stock units, options, warrants or rights are held by the undersigned pursuant to an agreement or equity awards granted under a stock incentive plan or other equity award plan, each such agreement or plan which is described in the Company’s Form 10-K for the fiscal year ended December 31, 2023 or subsequent filings with the SEC, or

(xi) pursuant to a bona fide third-party tender offer, merger, consolidation or other similar transaction that is approved by the Board of Directors of the Company and made to all holders of the Company’s capital stock involving a Change of Control¹ of the Company; provided that in the event that such tender offer, merger, consolidation or other similar transaction is not completed, the undersigned’s Lock-Up Securities shall remain subject to the provisions of this Letter Agreement;

provided that,

(b) exercise outstanding options, settle restricted stock units or other equity awards or exercise outstanding warrants pursuant to plans described in the Company’s Form 10-K for the fiscal year ended December 31, 2023 or subsequent filings with the SEC; provided that any Lock-up Securities received upon such exercise, vesting or settlement shall be subject to the terms of this Letter Agreement; provided that if the undersigned is required to make any filing under Section 16(a) of the Securities Exchange Act of 1934 (the “Exchange Act”), or other public filing, report or announcement during the

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Restricted Period, the undersigned shall clearly indicate in the footnotes thereto that the filing relates to the circumstances described in this clause and that the shares of Common Stock received upon the exercise or settlement, as applicable, of the stock option, warrant or restricted stock unit or other right or vesting event are subject to this Letter Agreement, and no public filing, report or announcement shall be voluntarily made; and

(c) establish trading plans pursuant to Rule 10b5-1 under the Exchange Act for the transfer of shares of Lock-Up Securities (each such plan, a “Trading Plan”); provided that (1) such Trading Plans do not provide for the transfer of Lock-Up Securities during the Restricted Period and (2) no filing by any party under the Exchange Act or other public announcement shall be required or made voluntarily in connection with such Trading Plan during the Restricted Period in contravention of this Lock-Up Agreement.

BENEFICIAL OWNERSHIP

If the undersigned is not a natural person, the undersigned represents and warrants that no single natural person, entity or “group” (within the meaning of Section 13(d)(3) of the Exchange Act) other than a natural person, entity or “group” (as described above) that has, or is controlled by a person that has, executed a Letter Agreement in substantially the same form as this Letter Agreement, beneficially owns, directly or indirectly, 50% or more of the common equity interests, or 50% or more of the voting power, in the undersigned.

TRANSFER AGENT

In furtherance of the foregoing, the Company, and any duly appointed transfer agent for the registration or transfer of the securities described herein, are hereby authorized to decline to make any transfer of securities if such transfer would constitute a violation or breach of this Letter Agreement.

POWER AND AUTHORITY

The undersigned hereby represents and warrants that the undersigned has full power and authority to enter into this Letter Agreement. All authority herein conferred or agreed to be conferred and any obligations of the undersigned shall be binding upon the successors, assigns, heirs or personal representatives of the undersigned.

NO AGENT RECOMMENDATION

The undersigned acknowledges and agrees that the Agent has not provided any recommendation or investment advice nor has the Agent solicited any action from the undersigned with respect to the Trade and the undersigned has consulted its own legal, accounting, financial, regulatory and tax advisors to the extent deemed appropriate. The undersigned further acknowledges and agrees that, although the Agent may be required or choose to provide certain Regulation Best Interest and Form CRS disclosures to the undersigned in connection with the Trade, the Agent is not making a recommendation to you to enter into this Letter Agreement, and nothing set forth in such disclosures is intended to suggest that the Agent are making such a recommendation.

MISCELLANEOUS

The undersigned hereby consents to receipt of this Letter Agreement in electronic form and understands and agrees that this Letter Agreement may be signed electronically. In the event that any signature is delivered by facsimile transmission, electronic mail, or otherwise by electronic transmission (including any electronic signature complying with the U.S. federal ESIGN Act of 2000, e.g., www.docusign.com) evidencing an intent to sign this Letter Agreement, such facsimile transmission, electronic mail or other electronic transmission shall create a valid and binding obligation of the undersigned with the same force and effect as if such signature were an original. Execution and delivery of this Letter Agreement by facsimile transmission, electronic mail or other electronic transmission is legal, valid and binding for all purposes.

[Signature page follows]

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This Letter Agreement and any claim, controversy or dispute arising under or related to this Letter Agreement shall be governed by and construed in accordance with the laws of the State of New York.

[Signature page to Lock-Up Agreement]